1. Field of the Invention
The present invention relates to a slurry used in a chemical mechanical polishing method, a method of manufacturing a semiconductor device and an apparatus of manufacturing a semiconductor device, particularly, to a slurry for a chemical mechanical polishing method that can be utilized for forming a buried wiring of a DRAM, a high speed logic LSI, etc., a method of manufacturing a semiconductor device using the particular slurry, and an apparatus of manufacturing a semiconductor device capable of utilizing the particular slurry.
2. Description of the Related Art
In recent years, miniaturization and improvement in the density of the device are being promoted in the field of semiconductor devices, and various fine processing technologies are being researched and developed. Particularly, a chemical mechanical polishing (CMP) technology is indispensable for forming a fine and high density buried wiring (damascene wiring).
The CMP technology includes a metal CMP technology that can be utilized for forming a buried wiring of a metal such as copper or aluminum. In the metal CMP technology, the polishing rate, the flatness and the scratch constitute important parameters in evaluating the CMP performance as described in the following. To be more specific, in order to improve the productivity of the semiconductor device, it is necessary to improve the polish processing rate (or through-put) of the metal CMP. Also, in order to suppress the elevation in the resistance value of the buried wiring, it is necessary to diminish as much as possible the excessive polishing amount (metal loss) of the buried wiring called dishing or thinning (or erosion). Further, in order to obtain with a high yield a semiconductor device in which a sufficient current flows through the buried wiring so as to allow the semiconductor device to operate as designed, it is necessary to decrease as much as possible to the density of the scratches generated in the buried wiring.
These properties are greatly dependent on the characteristics of the slurry and the polishing pad used in the CMP. For example, the CMP performance is related to, for example, the hardness of the polishing pad. In the main polish for polishing the metal used for forming a buried wiring, a hard pad having a high flatness is used in general as a pad.
On the other hand, the effect of the slurry for the CMP on the CMP performance are derived from, for example, the abrasive particles, the oxidizing agent or an additive contained in the slurry. Particularly, the characteristics of the abrasive particles give highly serious influences to the CMP performance. For example, the polishing rate is increased in general with increase in the size of the abrasive particles in the slurry.
The relationship between the characteristics of the slurry for the CMP and the CMP performance will now be described with reference to FIGS. 1A, 1B, 2A and 2B.
In general, a CMP slurry 7 contains a solvent 25 such as water, abrasive particles 18 such as alumina (Al2O3) particles or silica (SiO2) particles, and an oxidizing agent 22. As shown in FIG. 1A, the abrasive particles 18 are generally agglomerated within the solvent 25 of the slurry 7 so as to form an agglomerate (or secondary particle) 20. The polishing rate is increased with increase in the diameter of the agglomerate, i.e., the diameter of the secondary particle.
However, if the diameter of the secondary particle is increased, a deep dishing 108 tends to be generated in a metal wiring 26, as shown in FIG. 2A. Also, where the abrasive particles 19 are vigorously agglomerated and the secondary particle 20 is rendered excessively large, the abrasive particles 18 form a coarse particle. If a coarse particle is formed, a scratch 109 tends to be generated in applying the CMP to the metal formed of a relatively soft material such as aluminum.
On the contrary, where the abrasive particles 18 are sufficiently dispersed as shown in FIG. 1B, it is possible to suppress the generation of the dishing 108 in the metal wiring 26, as shown in FIG. 2B. In addition, the scratch 109 is unlikely to be generated. However, where the degree of dispersion of the abrasive particles 18 is increased, the polishing rate is markedly lowered. In other words, to suppress the generation of the dishing 108 and the scratch 109 has a trade-off relationship with the increase in the polishing rate.
It is considered reasonable to understand that the trade-off relationship noted above is generated as follows. In general, the polishing surface of the polishing pad used in performing the main polish referred to above has a roughness (or coarseness) of about 20 μm. The size of the abrasive grain is sufficiently small, compared with the roughness of the polishing surface of the polishing pad. Therefore, where the agglomerate 20 has a high degree of dispersion so as to provide an excessively large distance between the adjacent abrasive particles, the abrasive particles 18 is buried in the recessed portion on the surface of the polishing pad, with the result that each abrasive particles 18 fails to sufficiently interact with the metal wiring 26. It follows that, if the degree of dispersion of the agglomerate 20 is excessively high, the polishing power of the slurry 7 is lowered, which markedly lowers the polishing rate.
As described above, the degree of dispersion of the abrasive particles 18 seriously influences the CMP performance and, thus, it is important to control the degree of dispersion of the abrasive particles 18 to a desired value. However, the agglomerated state of the abrasive particles 18 tends to be changed with time. For example, if the CMP slurry 7 is stored without being used, the number of coarse particles is increased with time. To be more specific, where the slurry 7 is left to stand for a long time, the dishing 108 and the scratch 109 tend to be generated more easily. If the number of coarse particles is increased, the coarse particles are agglomerated so as to form a gigantic coarse particle. The agglomerated coarse particles are rendered incapable of floating in the solvent 25 so as to be precipitated. It is substantially impossible to disperse again the precipitated coarse particles in the solvent. In other words, the particular slurry is rendered substantially incapable of being used.
The oxidizing agent 22 contained in the CMP slurry 7 also tends to be decomposed. If decomposed, the oxidizing power of the oxidizing agent is markedly lowered. The oxidizing agent 22 whose oxidizing power has been lowered constitutes one of the main factors for bringing about the deterioration of the CMP performance such as the decrease in the polishing rate. In other words, the deterioration with time of the oxidizing agent 22 also causes the shortening in the life of the slurry 7.